Re: [Qemu-devel] [PATCH v2] spapr: fallback to raw mode if best compat mode cannot be set during CAS

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 3624 bytes --]

On Thu, Aug 17, 2017 at 01:23:50PM +0200, Greg Kurz wrote:
> KVM PR doesn't allow to set a compat mode. This causes ppc_set_compat_all()
> to fail and we return H_HARDWARE to the guest right away.
> 
> This is excessive: even if we favor compat mode since commit 152ef803ceb19,
> we should at least fallback to raw mode if the guest supports it.
> 
> This patch modifies cas_check_pvr() so that it also reports that the real
> PVR was found in the table supplied by the guest. Note that this is only
> makes sense if raw mode isn't explicitely disabled (ie, the user didn't
> set the machine "max-cpu-compat" property). If this is the case, we can
> simply ignore ppc_set_compat_all() failures, and let the guest run in raw
> mode.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> v2: - initialize raw_mode_supported to silent patchew

I hesitated about this, because making guest visible changes based on
host abilities can get really messy.  However we already have a bunch
of things like that in CAS, and we already migrate the compatibility
state, so I think it should be ok.

Applied to ppc-for-2.11.

> ---
>  hw/ppc/spapr_hcall.c |   18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 07b3da8dc4cd..2f4c4f59e110 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1441,7 +1441,8 @@ static target_ulong h_signal_sys_reset(PowerPCCPU *cpu,
>  }
>  
>  static uint32_t cas_check_pvr(sPAPRMachineState *spapr, PowerPCCPU *cpu,
> -                              target_ulong *addr, Error **errp)
> +                              target_ulong *addr, bool *raw_mode_supported,
> +                              Error **errp)
>  {
>      bool explicit_match = false; /* Matched the CPU's real PVR */
>      uint32_t max_compat = spapr->max_compat_pvr;
> @@ -1481,6 +1482,8 @@ static uint32_t cas_check_pvr(sPAPRMachineState *spapr, PowerPCCPU *cpu,
>          return 0;
>      }
>  
> +    *raw_mode_supported = explicit_match;
> +
>      /* Parsing finished */
>      trace_spapr_cas_pvr(cpu->compat_pvr, explicit_match, best_compat);
>  
> @@ -1499,8 +1502,9 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
>      sPAPROptionVector *ov1_guest, *ov5_guest, *ov5_cas_old, *ov5_updates;
>      bool guest_radix;
>      Error *local_err = NULL;
> +    bool raw_mode_supported = false;
>  
> -    cas_pvr = cas_check_pvr(spapr, cpu, &addr, &local_err);
> +    cas_pvr = cas_check_pvr(spapr, cpu, &addr, &raw_mode_supported, &local_err);
>      if (local_err) {
>          error_report_err(local_err);
>          return H_HARDWARE;
> @@ -1510,8 +1514,14 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
>      if (cpu->compat_pvr != cas_pvr) {
>          ppc_set_compat_all(cas_pvr, &local_err);
>          if (local_err) {
> -            error_report_err(local_err);
> -            return H_HARDWARE;
> +            /* We fail to set compat mode (likely because running with KVM PR),
> +             * but maybe we can fallback to raw mode if the guest supports it.
> +             */
> +            if (!raw_mode_supported) {
> +                error_report_err(local_err);
> +                return H_HARDWARE;
> +            }
> +            local_err = NULL;
>          }
>      }
>  
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]